Getting Gold: a practical treatise for prospectors, miners and students eBook

This should be used more for ascertaining relatively
large differences in altitudes than for purposes where
any great nicety is required. For hills under
2000 ft., the following rule will give a very close
approximation, and is easily remembered, because 55
degrees, the assumed temperature, agrees with 55 degrees,
the significant figures in the 55,000 factor, while
the fractional correction contains two fours.

Observe the altitudes and also the temperatures on
the Fahrenheit thermometer at top and bottom respectively,
of the hill, and take the mean between them.
Let B represent the mean altitude and b the mean temperature.
Then 55000 X B — b/B + b = height of the hill
in feet for the temperature of 55 degrees. Add
1/440 of this result for every degree the mean temperature
exceeds 55 degrees; or subtract as much for every
degree below 55 degrees.

TO DETERMINE HEIGHTS OF OBJECTS

By Shadows

Set up vertically a stick of known length, and measure
the length of its shadow upon a horizontal or other
plane; measure also the length of the shadow thrown
by the object whose height is required. Then it
will be:—­As the length of the stick’s
shadow is to the length of the stick itself, so is
the length of the shadow of the object to the object’s
height.

By Reflection

Place a vessel of water upon the ground and recede
from it until you see the top of the object reflected
from the surface of the water. Then it will be:—­As
your horizontal distance from the point of reflection
is to the height of your eye above the reflecting
surface, so is the horizontal distance of the foot
of the object from the vessel to its altitude above
the said surface.

Instrumentally

Read the vertical angle, and multiply its natural
tangent by the distance between instrument and foot
of object; the result is the height.

When much accuracy is not required vertical angles
can be measured by means of a quadrant of simple construction.
The arc AB is a quadrant, graduated in degrees from
B to A; C, the point from which the plummet P is suspended,
being the centre of the quadrant.

When the sights AC are directed towards any
object, S, the degrees in the arc, BP, are the measure
of the angle of elevation, SAD, of the object.

TO FIND THE DEPTH OF A SHAFT

Rule:—­Square the number of seconds
a stone takes to reach the bottom and multiply by
16.

Thus, if a stone takes 5 seconds to fall to the bottom
of a shaft—­

5 squared = 25; and 25 X 16 = 400 feet, the required
depth of shaft.

DESCRIPTION OF PLAN FOR RE-USING WATER

Where water is scarce it may be necessary to use it
repeatedly. In a case of this kind in Egypt,
the Arab miners have adopted an ingenious method which
may be adapted to almost any set of conditions.
At a is a sump or water-pit; b is an inclined plane
on which the mineral is washed and whence the water
escapes into a tank c; d is a conduit for taking the
water back to a; e is a conduit or lever pump for raising
the water. A certain amount of filtration could
easily be managed during the passage from c to a.